Catalyst comprising a metalic support and process for the production of olefins

ABSTRACT

A catalyst capable of supporting combustion beyond the fuel rich limit of flammability comprising a catalytic component and a metallic support wherein the support is a metallic structured packing comprising a multiplicity of open-ended channels and which has been loaded with a non metallic coating, and a process for the production of an olefin, said process comprising passing a mixture of a hydrocarbon and an oxygen-containing gas over said catalyst to produce an olefin.

The present invention relates to a process for the production of olefinsfrom hydrocarbons in which the hydrocarbons are treated to autothermalcracking.

Autothermal cracking is a route to olefins in which the hydrocarbon feedis mixed with oxygen and passed over an autothermal cracking catalyst.The autothermal cracking catalyst is capable of supporting combustionbeyond the fuel rich limit of flammability. Combustion is initiated onthe catalyst surface and the heat required to raise the reactants to theprocess temperature and to carry out the endothermic cracking process isgenerated in situ. Generally the hydrocarbon feed and the oxygen ispassed over a supported catalyst to produce the olefin product.Typically, the catalyst comprises at least one platinum group metal, forexample, platinum. The autothermal cracking process is described in EP332289B; EP-529793B; EP-A-0709446 and WO 00/14035.

The catalyst supports are usually non metallic and are typically ceramicmaterials, usually in the form of foams, monoliths, pellets, beads,spheres, tablets and/or extrudates. However whilst generally beingchemically inert non metallic supports can often be unstable to thermaland physical shock which results in support cracking.

The catalyst support may also be metallic. Due to their malleable naturemetallic supports do not exhibit support cracking but are oftenincapable of withstanding excessive front face temperatures that areproduced in the autothermal reactor which leads to oxidation andcorrosion.

Consequently there is a need to provide an improved support that is bothchemically inert and thermally stable.

It has now been found that the autothermal cracking process can beimproved by employing a catalyst with a modified metallic support andwhich has a structure that provides a low pressure drop in theautothermal reactor.

Accordingly, the present invention provides a catalyst capable ofsupporting combustion beyond the fuel rich limit of flammabilitycomprising a catalytic component and a metallic support wherein thesupport is a metallic structured packing comprising a multiplicity ofopen-ended channels and which has been loaded with a non metalliccoating.

The present invention also provides a process for the production of anolefin, said process comprising passing a mixture of a hydrocarbon andan oxygen-containing gas over a catalyst as herein described above toproduce said olefin.

Preferably, the catalyst component comprises a Group VIIIB metal.Suitable Group VIIIB metals include platinum, palladium, ruthenium,rhodium, osmium and iridium. Preferably, the Group VIIIB metal isselected from rhodium, platinum, palladium or mixtures thereof.Especially preferred are platinum, palladium or mixtures thereof.Typical Group VIIIB metal loadings range from 0.01 to 50 wt %,preferably, from 0.01 to 20 wt %, and more preferably, from 0.01 to 10wt %, for example 1-5 wt %, such as 3-5 wt %. Suitably, the firstcatalyst bed comprises platinum or palladium, especially platinum.

Preferably the catalyst component may be a promoted catalyst componentsuch as a promoted Group VIIIB metal catalyst. The promoter may beselected from the elements of Groups IIIA, IVA and VA of the PeriodicTable and mixtures thereof. Alternatively, the promoter may be atransition metal; the transition metal being a different metal to thecatalyst component, such as the Group VIIIB metal(s) employed as thecatalytic component.

The promoter may also be selected from any of the lanthanide metaloxides.

Preferred Group IIIA metals include Al, Ga, In and Tl. Of these, Ga andIn are preferred. Preferred Group IVA metals include Ge, Sn and Pb. Ofthese, Ge and Sn are preferred, especially Sn. The preferred Group VAmetal is Sb. The atomic ratio of Group VIIIB metal to the Group IIIA,IVA or VA metal may be 1:0.1-50.0, preferably, 1:0.1-12.0, such as1:0.3-5.

Suitable transition metal promoters may be selected from any one or moreof Groups IB to VIIIB of the Periodic Table. In particular, transitionmetals selected from Groups IB, IIB, VIIB, VIIB and VIIIB of thePeriodic Table are preferred. Examples of such transition metalpromoters include V, Ni, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir,Ni, Pt, Cu, Ag, Au, Zn, Cd and Hg. Preferred transition metal promotersare Mo, Rh, Ru, Ir, Pt, Cu and Zn, especially Cu. The atomic ratio ofthe Group VIIIB metal to the transition metal promoter may be1:0.1-50.0, preferably, 1:0.1-12.0.

Specific examples of promoted Group VIIIB metals for use as the promotedcatalyst component include Pt/Ga, Pt/In, Pt/Sn, Pt/Ge, Pt/Cu, Pd/Sn,Pd/Ge, Pd/Cu and Rh/Sn. Where the Group VIIIB metal is Rh, Pt or Pd, theRh, Pt or Pd may comprise between 0.01 and 5.0 wt %, preferably, between0.01 and 3.0 wt %, and more preferably, between 0.5 and 3.0 wt-% of thetotal weight of the catalyst. The atomic ratio of Rh, Pt or Pd to theGroup IIIA, IVA, VA or transition metal promoter may be 1:0.1-50.0,preferably, 1:0.1-12.0. For example, atomic ratios of Rh, Pt or Pd to Snmay be 1:0.1 to 50, preferably, 1:0.1-12.0, more preferably, 1:0.2-5.0and most preferably, 1:0.3-5.0. Atomic ratios of Pt or Pd to Ge may be1:0.1 to 50, preferably, 1:0.1-12.0, and more preferably, 1:0.5-8.0.Atomic ratios of Pt or Pd to Cu may be 1:0.1-3.0, preferably, 1:0.2-2.0,and more preferably, 1:0.5-1.5.

For the avoidance of doubt, the catalyst component and the promoter maybe present in any form, for example, as a metal, or in the form of ametal compound, such as an oxide.

The metallic support may be selected from any suitable metal. Suitablemetals may include steel (mild and high carbon), stainless steel,Hastaloy, Ni-Chrome, Inconel, Monel, nickel, copper, iron, platinum,noble metals and their alloys, cobalt, FeCrAlY, NiCrAlY, or any alloycontaining Y, Cr, Fe, Ni and Al e.g Kanthal, Incoloy MA956, or CoCrAlY.Small amounts of other elements, such as Si, Ti, Nb, Mo, W, Zr, Mg, Cu,may also be present.

Preferably the metal has a melting point of greater than 1200° C. andmost preferably the metal is selected from FeCrAlY, NiCrAlY, CoCrAlY,Ni-Chrome and (any grade of) Inconel and Monel.

The metallic support is a metallic structured packing which comprises amultiplicity of open-ended channels. This structure provides a lowpressure drop compared to other types of support, such as extrudates andpellets; when used in an autothermal reactor. This is advantageous sincehigh pressure drop in the autothermal reactor can lead to excessiveforce being applied to the catalyst, which can lead to structuralcollapse.

The metallic support may be in the form of a foam but is preferably inthe form of a channeled monolith.

The structural dimensions of the support type may also vary.

Wherein the support is in the form of a foam, the foams usually have apore size in the range of 10 pores per inch (ppi) to 100 ppi andpreferably between 30 to 45 ppi. These foams typically have a density offrom between 60% to 99% of theoretical density of a fully densematerial.

Wherein the support material is in the form of a monolith the monolithis usually provided with regular channels. These channels may be of anysuitable shape the preferred ones being square, rectangular, triangular,hexagonal and circular. Preferably the monolith is a honeycomb monolith.Typically the channels do not pass directly through the monolith andusually the channels provide a complex passageway through the monolith.Usually the monolith has between 2000 cpi (cells per inch) to 5 cpi andpreferably between 1000 cpi to 10 cpi.

The support preferably comprises a series of blocks or layers thattessellate together to leave no gaps. Preferably these blocks or layersare tiled within the reactor in different directions and most preferablyin a manner such that tiles of a layer either above or below do notexactly overlap with any neighbouring layer.

The non metallic coating is usually a ceramic material which may be anyoxide or combination of oxides that is stable at high temperatures of,for example, between 600° C. and 1200° C. The ceramic materialpreferably has a low thermal expansion co-efficient, and is resistant tophase separation at high temperatures.

Suitable ceramic materials include alumina, silica-alumina, acombination of alumina and mullite, lithium aluminium silicate,cordierite, silicon carbide, zirconia toughened alumina, partiallystabilized zirconia, fully stabilized zirconia, spinel, chromia,titania, aluminium titanate, or any combination of the above.

The non metallic coating may be loaded onto the metallic support by anymethod known in the art. In particular the non-metallic coating may beloaded onto the support by any one of the following methods;aluminizing, chemical vapour deposition, sputter coating andwashcoating.

Wherein the non metallic coating is alumina, aluminizing depositsaluminium metal onto the surface layer of the metallic support. Usuallyaluminizing comprises heating the metallic support in a cnicible withaluminium powder. The aluminium deposited upon the surface of themetallic support is then oxidized to form alumina.

Wherein chemical vapour deposition is used to provide a non-metalliccoating on the metallic support this usually involves the thermaldecomposition of a volatile material onto the surface of a heatedmetallic support.

Wherein sputter coating is used to provide a non-metallic coating on themetallic support the metallic support is spray coated with a fineparticulate material which typically contains some sort of binder suchthat it sticks to the surface of the support. Sputter coating may beperformed by arc or laser ablation.

In a preferred embodiment of the invention washcoating is used toprovide a non-metallic coating on the metallic support. Washcoatinginvolves providing a slurry of the non metallic coating which is thenpoured through/over the metallic support. Typically the slurry of thenon metallic coating is a ceramic coating and is preferably an aluminacolloidal suspension with a carefully defined viscosity and particlesize.

Wherein aluminizing is used the thickness of the non metallic coating isusually between 10-200 μm and preferably between 50-100 μm.

Wherein sputter coating is employed the thickness of the non metalliccoating is usually between 10 μm-2 mm and preferably between 0.1-1 mm.

Usually the % weight of coating relative to the weight of support isless than 5 wt %, and preferably less than 3 wt %.

Preferably substantially all of the metallic support is coated with thenon metallic coating.

The catalyst component employed in the present invention may be loadedonto the coated metal support by any method known in the art. Forexample, gel methods and wet-impregnation techniques may be employed.Typically, the support is impregnated with one or more solutionscomprising the metals, dried and then calcined in air. The support maybe impregnated in one or more steps. Preferably, multiple impregnationsteps are employed. The support is preferably dried and calcined betweeneach impregnation, and then subjected to a final calcination,preferably, in air. The calcined support may then be reduced, forexample, by heat treatment in a hydrogen atmosphere.

Preferably when the catalyst is positioned within the autothermalcracking reactor a non catalytic resistance zone is located upstream ofthe catalyst. The resistance zone usually comprises a network ofcapillaries or channels and most preferably the resistance zonecomprises a porous material and advantageously the porous material is anon metal e.g. a ceramic material. Suitable ceramic materials includelithium aluminium silicate (LAS), alumina (α-Al₂O₃), yttria-stabilisedzirconia, alumina titanate. A preferred porous material is alphaalumina. The porous material may be in the form of spheres, othergranular shapes or ceramic foams. Typically the resistance zone hasbetween 10-60 pores per square inch, preferably between 20-50 pores persquare inch and most preferably between 30-45 pores per square inch.

The process of the present invention may be used to convert both liquidand gaseous hydrocarbons into olefins. Suitable liquid hydrocarbonsinclude naphtha, gas oils, vacuum gas oils and mixtures thereof.Preferably, however, gaseous hydrocarbons such as ethane, propane,butane and mixtures thereof are employed. Suitably, the hydrocarbon is aparaffin-containing feed comprising hydrocarbons having at least twocarbon atoms.

The hydrocarbon feed is mixed with any suitable oxygen-containing gas.Suitably, the oxygen-containing gas is molecular oxygen, air, and/ormixtures thereof. The oxygen-containing gas may be mixed with an inertgas such as nitrogen or argon.

Additional feed components may be included, if so desired. Suitably,hydrogen, carbon monoxide, carbon dioxide or steam may be co-fed intothe reactant stream.

Any molar ratio of hydrocarbon to oxygen-containing gas is suitableprovided the desired olefin is produced in the process of the presentinvention. The preferred stoichiometric ratio of hydrocarbon tooxygen-containing gas is 5 to 16, preferably, 5 to 13.5 times,preferably, 6 to 10 times the stoichiometric ratio of hydrocarbon tooxygen-containing gas required for complete combustion of thehydrocarbon to carbon dioxide and water.

The hydrocarbon is passed over the catalyst at a gas hourly spacevelocity of greater than 10,000 h⁻¹, preferably above 20,000 h⁻¹ andmost preferably, greater than 100,000 h⁻. It will be understood,however, that the optimum gas hourly space velocity will depend upon thepressure and nature of the feed composition.

Preferably, hydrogen is co-fed with the hydrocarbon andoxygen-containing gas into the reaction zone. The molar ratio ofhydrogen to oxygen-containing gas can vary over any operable rangeprovided that the desired olefin product is produced. Suitably, themolar ratio of hydrogen to oxygen-containing gas is in the range 0.2 to4, preferably, in the range 1 to 3.

Hydrogen co-feeds are advantageous because, in the presence of thecatalyst, the hydrogen combusts preferentially relative to thehydrocarbon, thereby increasing the olefin selectivity of the overallprocess.

Preferably, the reactant mixture of hydrocarbon and oxygen-containinggas (and optionally hydrogen co-feed) is preheated prior to contact withthe catalyst. Generally, the reactant mixture is preheated totemperatures below the autoignition temperature of the reactant mixture.

Advantageously, a heat exchanger may be employed to preheat the reactantmixture prior to contact with the catalyst. The use of a heat exchangermay allow the reactant mixture to be heated to high preheat temperaturessuch as temperatures at or above the autoignition temperature of thereactant mixture. The use of high pre-heat temperatures is beneficial inthat less oxygen reactant is required which leads to economic savings.Additionally, the use of high preheat temperatures can result inimproved selectivity to olefin product. It has also been found that theuse of high preheat temperatures enhances the stability of the reactionwithin the catalyst thereby leading to higher sustainable superficialfeed velocities, and also reduces the thermal gradient experiencedacross the catalyst.

The process of the present invention may suitably be carried out at acatalyst exit temperature in the range 600° C. to 1200° C., preferably,in the range 850° C. to 1050° C. and, most preferably, in the range 900°C. to 1000° C.

The process of the present invention is usually operated at a pressureof greater than 0.5 barg. Preferably the autothermal cracking process isoperated at a pressure of between 0.5-40 barg and advantageously between10-30 barg e.g. 15-25 barg.

The reaction products are preferably quenched as they emerge from thereaction chamber to avoid further reactions taking place. Usually theproduct stream is cooled to between 750-600° C. within less than 100milliseconds of formation, preferably within 50 milliseconds offormation and most preferably within 20 milliseconds of formation e.g.within 10 milliseconds of formation.

Wherein the autothermal cracking process is operated at a pressure of5-20 barg usually the products are quenched and the temperature cooledto between 750-600° C. within 20 milliseconds of formation.Advantageously wherein the autothermal cracking process is operated at apressure of greater than 20 barg the products are quenched and thetemperature cooled to between 750-600° C. within 10 milliseconds offormation.

The invention will now be illustrated by the following examples.

EXAMPLES

Preparation of Catalysts

Comparative Catalyst 1

FeCrAlY foam blocks, comprising (by weight) approximately 73% iron, 20%chromium, 5% aluminium and 2% yttrium (III) oxide, in the shape ofcylinders having dimensions of 15 mm diameter by 25 mm depth, and poresize of 30 pores per inch (ppi) were purchased from Porvair AdvancedMaterials.

The foams were repeatedly impregnated by immersion in a solution oftetraamineplatinum (II) chloride and copper (II) nitrate hekahydrate,said solution containing sufficient of each respective salt to achieve anominal Pt loading of 3 wt % and a nominal Cu loading of 1 wt % if allthe metal in the respective salts were incorporated into the finalcatalyst formulation:

Between impregnations excess solution was removed from the foams, whichwere then dried in air at ca. 120° C. for approximately 20 minutes.After all the metal salts had been incorporated the foams were calcinedin air at 600° C. for approximately 6 hours, cooled to room temperature,and then reduced under a flow of 50 vol % hydrogen/50 vol % nitrogen at750° C. and at a flow rate of 2 nl/min for 1 hour.

Catalyst A

As for Catalyst 1, FeCrAlY foam blocks comprising (by weight)approximately 73% iron, 20% chromium, 5% aluminium and 2% yttrium (III)oxide, in the shape of cylinders having dimensions of 15 mm diameter by25 mm depth, and having a pore size of 30 pores per inch (ppi) werepurchased from Porvair Advanced Materials.

The foams were washcoated with a gamma alumina washcoat and calcinedbefore being loaded with Pt and Cu at a nominal Pt loading of 3 wt % anda nominal Cu loading of 1 wt % (assuming all the metal were incorporatedinto the final catalyst formulation).

The foams were subsequently calcined in air at 600° C. for approximately6 hours, cooled to room temperature, and then reduced under a flow of 50vol % hydrogen/50 vol % nitrogen at 750° C. and at a flow rate of 2nl/min for one hour.

Catalyst Testing

Catalyst testing was performed at atmospheric pressure (0 barg) in anautothermal reactor comprising a steel reactor in an electrically heatedfurnace.

The catalyst blocks were positioned in the reactor between two LAS heatshields. Two blocks of catalyst were loaded in sequential fashion intothe reactor for each test, to give a total catalyst bed of 50 mm depth,and the reactor heated to 850° C. Ethane (6.09 nl/min), hydrogen (5.48nl/min), nitrogen (1.61 nl/min) and oxygen (2.74 nl·min) were suppliedfrom cylinders via mass flow controllers into two manifolds, one foroxygen, the second for the other gases. The two gas streams werepre-heated to around 100° C. and then mixed immediately before thecatalyst. The product gases were sampled and analysed by gaschromatography. The results are shown in Table 1 and Table 2. TABLE 1Ethylene yield (g/100 g hydrocarbon) with time on stream for ComparativeCatalyst 1 and Catalyst A. Ethylene yield (g/100 g) Time on stream hoursComparative Catalyst 1 Catalyst A 1.75 — 56.6 2.5 51.5 — 4.75 51.35 —5.0 — 56.7 9.25 52.3 — 21.75 — 56.4 25.2 54.5 — 26.0 — 56.3 32.0 54.3 —44.5 — 56.6 48.0 — 56.7 48.5 55.0 — 51.7 — 56.7 52.7 55.44 — 58.3 53.4 —68.5 — 56.6 72.2 55.2 — 74.4 — 56.1

TABLE 2 Product distribution at 48 hours on stream for ComparativeCatalyst 1 and Catalyst A. Comparative Catalyst 1 Catalyst A EthaneConversion (%) 78.8 81.0 Yield (g/100 g hydrocarbon): Hydrogen 7.60 7.10Water 40.2 43.2 Methane 5.27 6.71 CO 14.2 14.8 CO2 5.68 1.58 Ethylene55.0 56.7 Ethane 21.2 19.0 Acetylene 0.58 0.94

Table 1 shows that, relative to a non-washcoated metallic foam, CatalystA results in an increased ethylene yield. Table 2 shows that, relativeto a non-washcoated metallic foam, and in addition to an increasedethylene yield, Catalyst A also results in a significantly reducedcarbon dioxide yield.

1-14. (canceled)
 15. A process for the production of an olefin, saidprocess comprising passing a mixture of a hydrocarbon and anoxygen-containing gas over a catalyst capable of supporting combustionbeyond the fuel rich limit of flammability, said catalyst comprising acatalytic component and a metallic support wherein the support is ametallic structured packing comprising a multiplicity of open-endedchannels and which has been loaded with a non metallic coating.
 16. Aprocess as claimed in claim 15, wherein the catalyst component comprisesa Group VIIIB metal.
 17. A process as claimed in claim 15, wherein themetallic support is selected from FeCrAlY, NiCrAlY, CoCrAlY, Ni-Chrome,Inconel and Monel.
 18. A process as claimed in claim 15, wherein themetallic support is in the form of a foam having a pore size in therange of 10 pores per inch (ppi) to 1 Ooppi.
 19. A process as claimed inclaim 15, wherein the metallic support is in the form of a monolithhaving between 2000 cpi (cells per inch) to 5 cpi.
 20. A process asclaimed in claim 15, wherein the metallic support comprises a series ofblocks or layers that tessellate together to leave no gaps.
 21. Aprocess as claimed in claim 15, wherein the non metallic coating is aceramic material selected from alumina, silica-alumina, a combination ofalumina and mullite, lithium aluminium silicate, cordierite, siliconcarbide, zirconia toughened alumina, partially stabilized zirconia,fully stabilized zirconia, spinel, chromia, titania, aluminium titanate,or any combination of the above.
 22. A process as claimed in claim 15,wherein hydrogen is co-fed with the hydrocarbon and oxygen-containinggas to the reaction zone.
 23. A process as claimed in claim 15, whereina non catalytic resistance zone is located upstream of the catalyst. 24.A process as claimed in claim 15, wherein the ratio of hydrocarbon tooxygen-containing gas is 5 to 16, times the stoichiometric ratio ofhydrocarbon to oxygen-containing gas required for complete combustion ofthe hydrocarbon to carbon dioxide and water.
 25. A process as claimed inclaim 15, wherein the process is operated at a pressure of between 10-30barg.